This invention relates to a new graft copolymer and to a process for producing same. More particularly, this invention relates to a graft copolymer composed of an ethylene/propylene/diene terpolymer backbone having a homopolymerized or copolymerized methacrylic ester graft moiety and to a process for producing same which comprises grafting a lower alkyl methacrylate alone or in mixture with an ethylenically unsaturated monomer or monomers copolymerizable therewith to an ethylene/propylene/diene terpolymer.
In general, the properties of polymers can be modified more or less by grafting a monomeric component to the polymers and the resulting graft copolymers are themselves useful as moldable resins with improved properties for further processing or are suitable, in combination with a proper vehicle, as a treating agent for resins, metals, fibers, glass and the like materials or as a binder for these materials. In fact, the graft polymerization of methyl methacrylate to natural rubber is adopted in the prior art as a means for improving the physical and electrical properties of natural rubber at high temperatures. However, such known graft copolymer was not satisfactory in thermoageing-resisting, weather-resisting and ozone-resisting properties because of the reason that the natural rubber structure constituting the backbone of such natural rubber-methyl methacrylate graft copolymer contains unsaturated bonds.
In order to overcome such disadvantages, many studies have been undertaken and the use of unsaturated bond-free polymers such as chlorinated polyethylene, ethylene/vinyl acetate copolymer, poly(acrylic ester), ethylene/propylene copolymer and poly-isobutylene have been considered as backbone rubbery polymer. However, due to difficulty of graft copolymerization of vinyl monomers to saturated rubbery polymers, the problem has not been solved yet. On the other hand, the graft copolymerization of vinyl monomers to the ethylene/propylene/non-conjugated diene terpolymer is also known. Since this terpolymer is also a saturated rubbery polymer, the graft copolymerization of vinyl monomers to such saturated rubbery polymers hardly takes place. In the prior art techniques, therefore, such graft copolymerization with vinyl monomer is usually carried out after compulsorily oxidizing the saturated backbone polymer with ozone-containing oxygen, oxygen or air under heating (60.degree.-100.degree.C) and then to graft copolymerize the vinyl monomer. (For example, see Japanese Patent Publns. Nos. 16911/65, 6058/68 and 24344/70.
However, such oxidation processes are not desirable because the oxidation of a saturated backbone polymer takes such a long period of time as 2-8 hours and it takes as a whole a considerable period of time until the final product is obtained. In addition, such process involves a number of steps and incurs degradation of the backbone polymer by oxidation.
Thus, there is a great demand for developing a new type graft copolymer which can entirely overcome the drawbacks seen in the prior art graft copolymers.